Blasting cap with field-attached lead wires



April `20, 1965 G. L. GRIFFITH 3,179,050

BLASTING CAP WITH FIELD-ATTACHED LEAD WIRES Filed Sept. ll, 1963 1| .l [..Illll vvvvYvvvvvvvvvvvvvvvvvvvvvvv FIG. 3

Inven to r:

George L. Griffith FIG.

FIG. 2

United States Patent O 3,179,050 BLASTING CAP WITH FIELD-ATTACHED LEAD WIRES George L. Griliith, Coopersburg, Pa., assigner to Trojan Powder Company, Allentown, Pa., a corporation Filed Sept. 11, 1963, Ser. No. 368,193 1 Claim. (Cl. 14n- 2.8)

This invention relates to electric blasting caps and has for its principal object the provision of a cap which, except for later-attached lead wires, may be completed at the factory and sent to the job site where appropriate lead wires of suitable length may readily be attached either at the place of use or at a small nearby assembly plant, the intent being to minimize the large inventories of blasting caps now required because of the great number of wire lengths.

An important feature of the invention is that the design permits mass production with conventional machinery at the factory and provides a device which insures positive contact with the later assembled lead wires without any soldering at that time. The rubber plug provides ample room for all parts to slide in place without the need for line tolerances.

A further object of the invention is to provide a water- I proof electrical blasting cap in which there is no need for expanding holes in the plug or to make certain dimensions critical, as the waterproof-lit and the proper rnechanical joint are obtained in the present case by operations making it substantially impossible to pull out the wires or to incur danger of water leakage.

In the drawings:

FIGURE 1 is a central section;

FIGURE 2 is a perspective view of the inside of a sleeve;

FIGURE 3 is an enlarged sectional view of the end ci the blasting cap as it leaves the factory.

In FIGURE l of the drawings the shell or casing is of suitable material, preferably metal, having the usual closed bottom and open top. The shell contains an explosive charge which may include a base charge Il, an initiating charge 12 and an ignition charge 14 in which is located the resistance bridge wire 15 secured in any ordinary manner to the leg wires 16 carried by a bridge plug 17. A rubber plug 20 which may or may not be integral with bridge plug 17 extends to the open end 2l of the casing and has axial holes 22 which are enlarged as at 23 to provide bores 24 to receive loosely the insulated ends of copper lead wires 30 of about 20 gauge carrying vinyl insulation 25 which may also be applied to the exposed face of plug 20 to aid in insuring a waterproof closure for the open end of the shell and the blasting cap.

The ends of the leg wires 16 are soldered inside a pair of split bronze sleeves 26 which have one-way prongs 27 such as in a grater, as shown in perspective in FIGURE 2. The sleeves 26 thus lightly closed on and soldered to the leg wires 16 are positioned in the holes 22 approximately to the level of the shoulder 23 between the holes 22 and the slightly larger bores 24.

llgl) Patented Apr. 20, 1965 ICC With the members in this position the casing is crimped at the factory as at 32 thus eiiectively sealing the leg wires 16 in the bridge plug 17 and the blasting cap is ready for shipment to the place of use, plug 20 being in place (whether or not integral with plug 17) and ready for reception of lead wires 30 of suitable length.

At the place of use or in a nearby small assembly plant the inside lead wires 30 of proper length and having bare ends somewhat shorter than the length of the sleeves 26, are now inserted in the bores 24 and 22. As the bare ends enter the sleeves readily, the prongs 27 readily allowing passage in that direction but not in the opposite direction and the insulated portion of these wires sliding somewhat freely in the larger bores 24, the blasting cap is ready for use except for the optional but preferred roll crimping as at 33 to insure positive contact of the split sleeves with the bare ends of the lead Wires and the roll crimping as at 34 which makes a waterproof seal about the insulated portion of wires 30. The waterproofing as stated may be aided by an application of vinyl insulation by dipping or spraying to the connecting wires and to the exposed face 2l. of plug 2t) extending to the shell or casing.

What I claim is:

A blasting cap comprising a cylindrical shell open at one end and having therein an explosive charge, a resistance bridge wire in said charge, leg wires leading from the bridge wire, a pair of sleeves permanently secured at one end to said leg Wires, said sleeves being open at the other end to receive readily the bare ends of a pair of lead wires, and a cylindrical plug surrounding said sleeves and fitting said shell, said sleeves being slit and each carrying integral one-way prongs to prevent pulling the lead Wires out of the sleeves, said plug having two bores each of two different diameters and each coaxial with one of said split sleeves, the smaller diameter bores iitting tightly the split sleeves and the other bores being of slightly larger outside diameter to receive readily Aat a later time the insulated portion of a pair of lead wires which have bare ends to slide into the split sleeves as the insulated portions oi the lead wires slide Iin the larger diameter bores to guide the bare ends between the one-way prongs, whereby the blasting cap may be completed as claimed, at the factory, and appropriate lead wires of suitable length may easily and readily be attached at the place of use, thus minimizing the large inventories of blasting caps now required when the lead wires are secured at the factory.

Reerences Cited by the Examiner UNITED STATES PATENTS 1,568,585 1/26 Brune 339-95 2,722,155 11/55 Pauls 102-28 X 2,916,994 12/59 ONeill 102-28 3,008,117 1l/61 Feustel et al. 339-95 3,040,284 6/ 62 Connell.

FOREIGN PATENTS 1,095,725 12/60 Germany 102-28 i60,` SAMUEL FEINBERG, Primary Examiner. 

